The present invention relates to fuel injectors and, more particularly, to a method and apparatus for controlling a dual coil fuel injector.
Dual coil fuel injectors typically include a first coil for opening the injector valve and a second coil for closing the valve. The first or opening coil acts to open the valve against the force of a return spring, and the second or closing coil acts to close the valve when the opening coil is de-energized. The force of the closing coil is a predetermined amount less in magnitude than, and is therefore insufficient to overcome the force of, the opening coil. The closing coil can therefore be energized before the opening coil is de-energized in order to more fully develop the magnetic force of the closing coil prior to de-energizing the opening coil, thereby facilitating relatively rapid closing of the valve.
The coils are energized by the application thereto of respective electrical signals or pulses. The duration or width of the pulse applied to the closing coil, i.e., the closing coil pulse, is generally fixed. The duration or width of the pulse applied to the opening coil, i.e., the opening coil pulse, is varied dependent upon various engine operating parameters, such as, for example, engine speed and load. By varying the duration of the opening coil pulse, the fuel injector valve is held open for a period of time sufficient to ensure the required amount of fuel is injected for a particular set of engine operating conditions. As stated above, the closing coil may be energized a predetermined amount of time prior to the de-energizing of the opening coil to facilitate more rapid valve closing. Therefore, the pulses provided to the opening and closing coils xe2x80x9coverlapxe2x80x9d by approximately that predetermined amount of time, which is referred to hereinafter as the overlap. Generally, the overlap period is fixed, i.e., the same overlap period is applied to all injector events regardless of the duration or width of the opening coil pulse.
Applying a pulse to the closing coil that has a fixed overlap period relative to the opening pulse has certain undesirable consequences. As the width or duration of the opening pulse decreases the fixed overlap period constitutes a greater portion of the opening pulse duration, i.e., the closing pulse is applied earlier relative to the opening pulse. Thus, as the duration of the opening pulse decreases the relative overlap of the opening and closing coil pulses increases. As the duration of the opening pulse approaches the fixed overlap period, the valve may not have adequate time to fully open before the closing pulse is received and the closing coil energized. Energizing the closing coil before the injector valve is fully opened can result in the amount of fuel injected being less than desired for a given opening coil pulse duration. Further, there is a delay in time between the application of the opening pulse and the actual opening of the injector valve. This delay in valve or injector response is generally fixed and further restricts the lower limit of the opening pulse duration in order avoid injecting less fuel than desired.
The undesirable consequences of applying a fixed duration overlap are shown in the dashed FIXED OVERLAP line of FIG. 1, which illustrates that the fuel flow through the fuel injector xe2x80x9ctails off leanxe2x80x9d (i.e., fuel flow decreases in a generally exponential manner as the pulse width applied to the opening coil decreases) at xe2x80x9clow endxe2x80x9d operating conditions, i.e., opening coil pulses having relatively small pulsewidths of, for example, less than 0.9 milliseconds (mS). Thus, substantially less than the desired amount of fuel is injected when a fixed overlap is applied to the coils under these low-end operating conditions. Injecting less fuel than intended at low-end operating conditions can result in reduced engine power and/or rough engine operation.
Therefore, what is needed in the art is a method and apparatus for controlling a dual coil fuel injector that achieves improved flow performance from the fuel injector.
Furthermore, what is needed in the art is a method and apparatus for varying the overlap between the opening and closing pulses applied to a dual coil fuel injector.
Moreover, what is needed in the art is a method and apparatus that enables improved control over the amount of fuel injected at low-end operating conditions (i.e., shorter duration pulses being applied to the opening coil).
The present invention provides an apparatus and method for controlling a dual coil fuel injector.
The present invention comprises, in one form thereof, a method that includes issuing an opening coil pulse to the opening coil. The opening coil pulse has an opening coil pulse width (OCPW) and an opening coil turn on time (OCTOT). A closing coil turn on time (CCTOT) is calculated dependent at least in part upon the OCPW. A closing coil pulse is issued to the closing coil at the calculated CCTOT.
An advantage of the present invention is that the CCTOT is delayed relative to the OCTOT, thereby reducing the pulse overlap and achieving improved performance of the fuel injector.
Another advantage of the present invention is that the overlap between the opening and closing coil pulses is variable, thereby allowing the valve of the fuel injector to more fully respond to the opening coil pulse and prevent premature pinch off of fuel flow.
A further advantage of the present invention is improved control over the amount of fuel injected at low-end operating conditions.